Service Provider (SP) networks carry real-time traffic such as voice and video over Pseudowire (PW). Due to the type of data carried in SP networks, it is critical to minimize the traffic loss due to PW failure. PW redundancy is a mechanism in which a primary PW is protected by a backup PW. A primary and/or backup PW can be Single Segment Pseudowire (SS-PW) or Multi-Segment Pseudowire (MS-PW).
One method used to signal PW failure is to use a PW status message, which may be carried by the Label Distribution Protocol (LDP) or the Pseudowire-Operation Administration and Maintenance (PW-OAM) protocol to a destination terminating device (end points) of the PW (that is, when one end of the PW detects a failure, a PW status message may be sent from that end to another end to convey the failure to the other end.). While LDP messages are handled in control-plane, the PW-OAM protocol relies on the rapid transition of three messages followed by refresh messages that are sent in-band. If the initial messages do not reach the destination (e.g., due to network congestion), the destination of the PW status notification (terminating device) relies on the subsequent refresh message(s) to learn about the failure. As such, failure notification via PW status message may not always ensure carrier-grade protection (e.g., within sub-50 ms) for PW services, since the traffic loss due to failure depends on failure detection time, failure propagation time to the node hosting a backup PW, and backup PW activation time.
Another common method of detecting PW failures is to monitor the status of the underlying Label Switched Path (LSP) over which the PW runs. In this case, mechanisms associated with the control plane of the LSP (e.g., Resource reSerVation Protocol “RSVP”) can be used to detect the failure of the LSP, which in turn invokes the PW switch. Alternatively, LSP OAM and LSP fault management can be used to detect failure of the underlying LSP, which in turn invokes the PW switch. As with PW failure detection mechanisms in certain circumstances, however, a failure may not be detected in the LSP, so the PW affected is not switched to support carrier grade operations.